Millimeter Waves (mmWaves) are radio waves with wavelength in the range of 1 millimeter (mm)-10 mm, which corresponds to a radio frequency of 30 GigaHertz (GHz)-300 GHz. Per the definition by the International Telecommunications Union (ITU), these frequencies are also referred to as the Extremely High Frequency (EHF) band.
The mmWaves exhibit unique propagation characteristics. For example, compared with lower frequency radio waves, mmWaves suffer higher propagation loss, have a poorer ability to penetrate objects, such as buildings, walls, foliage, and are more susceptible to atmosphere absorption, deflection and diffraction due to particles (e.g., rain drops) in the air. On the other hand, due to the smaller wavelengths of the mmWaves, more antennas can be packed in a relatively small area, thereby allowing for the implementation of a high-gain antenna in small form factor.
The mmWaves have been less utilized than the lower frequency radio waves. A vast amount of spectrum is available in the mmWave band. For example, the frequencies around 60 GHz, which are typically referred to as the 60 GHz band, are available as unlicensed spectrum in most countries. This is one of the reasons that the mmWave spectrum has been proposed for cellular communications in the fifth generation (5G).
Several approaches have been proposed to take advantage from multiple antennas to increase data rate of wireless communication. For example, spatial multiplexing is a transmission technique in MIMO communication used to transmit independent and separately encoded data signals from each of the multiple antennas. Therefore, the space dimension is reused, or multiplexed, more than one time. However, due to large path loss in mmWave spectrum, the spatial multiplexing is impractical for the mmWaves transmission.
Spatial modulation is a transmission technique that uses an index of transmit antenna as an additional source of information to improve the overall spectral efficiency, see, e.g., WO2011104502. However, due to dense packing of antenna elements in the same aperture, the mmWave transmissions from different antennas can be indistinguishable from each other.
Accordingly, there is a need for a system and a method suitable for transmission in mmWave spectrum that can take advantage from multiple antennas to increase data rate.